content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.flowable.internal.subscribers;
  
  import java.util.NoSuchElementException;
  import java.util.concurrent.*;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.reactivestreams.Subscription;
  
  import hu.akarnokd.reactivestreams.extensions.RelaxedSubscriber;
  import io.reactivex.common.RxJavaCommonPlugins;
  import io.reactivex.common.internal.utils.BlockingHelper;
  import io.reactivex.flowable.internal.subscriptions.SubscriptionHelper;
  
  /**
   * A Subscriber + Future that expects exactly one upstream value and provides it
   * via the (blocking) Future API.
   *
   * @param <T> the value type
   */
  public final class FutureSubscriber<T> extends CountDownLatch
  implements RelaxedSubscriber<T>, Future<T>, Subscription {
  
      T value;
      Throwable error;
  
      final AtomicReference<Subscription> s;
  
      public FutureSubscriber() {
          super(1);
          this.s = new AtomicReference<Subscription>();
      }
  
      @Override
      public boolean cancel(boolean mayInterruptIfRunning) {
          for (;;) {
              Subscription a = s.get();
              if (a == this || a == SubscriptionHelper.CANCELLED) {
                  return false;
              }
  
              if (s.compareAndSet(a, SubscriptionHelper.CANCELLED)) {
                  if (a != null) {
                      a.cancel();
                  }
                  countDown();
                  return true;
              }
          }
      }
  
      @Override
      public boolean isCancelled() {
          return SubscriptionHelper.isCancelled(s.get());
      }
  
      @Override
      public boolean isDone() {
          return getCount() == 0;
      }
  
      @Override
      public T get() throws InterruptedException, ExecutionException {
          if (getCount() != 0) {
              BlockingHelper.verifyNonBlocking();
              await();
          }
  
          if (isCancelled()) {
              throw new CancellationException();
          }
          Throwable ex = error;
          if (ex != null) {
              throw new ExecutionException(ex);
          }
          return value;
      }
  
      @Override
      public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
          if (getCount() != 0) {
              BlockingHelper.verifyNonBlocking();
              if (!await(timeout, unit)) {
                  throw new TimeoutException();
              }
          }
  
          if (isCancelled()) {
              throw new CancellationException();
          }
  
          Throwable ex = error;
          if (ex != null) {
              throw new ExecutionException(ex);
          }
          return value;
      }
  
      @Override
      public void onSubscribe(Subscription s) {
          if (SubscriptionHelper.setOnce(this.s, s)) {
              s.request(Long.MAX_VALUE);
          }
      }
  
      @Override
      public void onNext(T t) {
          if (value != null) {
              s.get().cancel();
              onError(new IndexOutOfBoundsException("More than one element received"));
              return;
          }
          value = t;
      }
  
      @Override
      public void onError(Throwable t) {
          for (;;) {
              Subscription a = s.get();
              if (a == this || a == SubscriptionHelper.CANCELLED) {
                  RxJavaCommonPlugins.onError(t);
                  return;
              }
              error = t;
              if (s.compareAndSet(a, this)) {
                  countDown();
                  return;
              }
          }
      }
  
      @Override
      public void onComplete() {
          if (value == null) {
              onError(new NoSuchElementException("The source is empty"));
              return;
          }
          for (;;) {
              Subscription a = s.get();
              if (a == this || a == SubscriptionHelper.CANCELLED) {
                  return;
              }
              if (s.compareAndSet(a, this)) {
                  countDown();
                  return;
              }
          }
      }
  
      @Override
      public void cancel() {
          // ignoring as `this` means a finished Subscription only
      }
  
      @Override
      public void request(long n) {
          // ignoring as `this` means a finished Subscription only
      }
  }
  